1. Technical Field
The present invention relates to repeater-based communication systems in general, and in particular to satellite communication systems having communication links between satellites and earth stations. Still more particularly, the present invention relates to a method and apparatus for controlling uplink transmission power of an earth station within a satellite communication system.
2. Description of the Prior Art
A typical satellite communication system includes an earth-orbiting satellite and several earth stations. A standard communications technique is commonly utilized to establish signal paths between the satellite and each of the earth stations. The signal paths includes an uplink path in which signals are transmitted from an earth station to the satellite, and a downlink path in which signals are transmitted from the satellite to an earth station. Operating as a repeater, the satellite generates downlink signals by translating and amplifying uplink signals in order to establish signal paths. The part of the satellite that performs the repeater function is called a transponder, and the satellite usually has a limited amount of transponder power and bandwidth to allocate to downlink paths.
One particular problem encountered by satellite communication systems during satellite communications is weather elements. For example, rain, moisture laden clouds, and other atmospheric conditions may reduce the power of radio signal transmissions. This effect generally becomes more prominent for radio signal transmissions at higher frequencies. The typical frequencies utilized in satellite communications are as follows:
At these relatively high frequencies, the atmospheric effects can attenuate a signal enough to make a signal path unusable or even unavailable. Also, if changing weather causes the satellite to receive varying uplink signal power levels from a single earth station, all other earth stations that receives signals from the satellite will also be affected because of the limited ground station receive margin. Consequently, it would be desirable to provide an improved method and apparatus to control the uplink transmission power of an earth station within a satellite communication system.
In accordance with a preferred embodiment of the present invention, a satellite communication system includes a satellite and one or more earth stations one of which serving as a control station. The satellite can receive uplink signals from any one of the earth stations and retransmits the uplink signals as downlink signals, along with a beacon signal. The control station measures the power of the downlink signals and the beacon signal received from the satellite, and also measures the noise power near the beacon signal. From these measurements, the control station determines an appropriate gain value of the power for uplink transmissions for each of the earth stations.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.